He used some galvanized bolts as the source of zinc. It forms one pole of each cell, with a thin copper tube as the other pole. Each cell is rather weak, but when combined with others it makes a respectable battery. We’ve seen acidic fruit used to power LEDs, but [Ryan] wanted to do a little more. He built a circuit that would store electricity until he had enough potential to power an LED diode. After the break you can see a four second clip of the fruit wielding its new laser defense system.

It is not using the fruit to power the battery. It is using the fruit to supply the electrolyte for the battery. The redox reactions at the electrodes are where the power lies, not the electrolyte.

I’ve seen many science fair exhibits with batteries that use unconventional electrolytes, such as potatoes, lemons, seawater, etc. It’s a common mistake in the popular press to say that these are doing something like “getting energy from seawater”, or “energy from potatoes”. But the energy comes from the corrosion of the electrodes. The energy was originally put into the battery when the metal of the electrodes was refined. The expensive and energy-intensive part of a conventional battery isn’t the electrolyte, it’s the electrodes.

Yeah, and it’s a shame. Otherwise we could solve our energy problems AND remove the calories from our food at the same time! “I can eat all the bacon I want now! I just plug my phone into the fatty part and let it charge for a while…”